This invention relates to a projection lens, and more particularly, relates to a lens adapted to project an enlargement of an image appearing on a cathode ray tube (CRT) such as a screen of a television set.
Co-pending application Ser. No. 070,748 now U.S. Pat. No. 4,300,817 discloses a lens which comprises from the image end a first group which is an aperture dependent aberration corrector element of essentially no optical power, a second positive group providing essentially all of the positive power of the lens, and a third group which corrects for field curvature, and in some cases, distortion. The optical power of the first group as a ratio to unity power of the overall lenses is between 0.1 and 0.4.
Co-pending application Ser. No. 228,012 now U.S. Pat. No. 4,348,081 discloses a lens comprising from the image end a first group of positive power which also corrects aperture dependent aberrations, a second positive group, and a third group which corrects for field curvature, and in some cases, distortion. The powers of the groups K1, K2, and K3 are chosen in a range related to unity power of the overall lens as follows: EQU 0.25&lt;K1&lt;0.50 EQU 0.85&lt;K2&lt;1.2 EQU -1.3&lt;K3&lt;-0.9
In addition the elements of the groups may also have aspheric surfaces.
The present invention is a new and improved projection lens which is capable of providing a more compact lens than the projection lenses of the co-pending applications. The degree of compactness is accomplished in part by the internal folding of the optical axis of the projection lens.